Recent advances have been made in the field of hydrogel adhesives, particularly those adhesives that can be utilized on human skin. One intent of such adhesives is to provide consistent adhesion properties after subsequent detachments and re-attachments, while minimizing or eliminating the amount of adhesive residue left on the surface after each detachment. Such adhesives can involve the use of monomers and plasticizers, such as glycerol. Often, these adhesives are crosslinked using a procedure known as photopolymerization. Unfortunately, the use of such monomers and photopolymerization can often result in levels of residual monomer that are unknown until after the adhesive is prepared. Additionally, the photopolymerization procedure can produce toxic by-products, such as acrolein, when used in combination with glycerol. Therefore, there is a need for an adhesive composition which is based on a polymer with specified low levels and/or known levels of residual monomer, and which does not result in the production of toxic by-products.
Furthermore, the production of hydrogel adhesives such as those described above can be very cost-intensive. For example, such processes typically involve ultraviolet (UV) polymerization which requires, among other things, nitrogen purging and expensive UV lamps and photoinitiators. UV polymerized hydrogel adhesives are generally formed in unit sizes because the low viscosity monomers must be confined in a cell until the polymerization is complete. Therefore, there is a further desire for an adhesive composition made using a procedure that is less complex, that has lower capital requirements for a drying operation, and that is more amenable to large scale coating and drying with subsequent die cutting to shape.
A further issue with hydrogel adhesives such as those described above concerns the amount of water contained in the adhesives. For example, such hydrogel adhesives typically contain at least 10% water and as much as 85% water by weight. This high water content may be an issue because evaporation of the water, whether in storage or in use, can result in significant changes in the adhesion properties of the hydrogel adhesive. For instance, drying during storage can result in stiff adhesives with poor tack and compliance. Additionally, drying during use can result in significant adhesive build and painful removal. Therefore, there is a further need for an adhesive composition that contains very little water, thus minimizing water loss induced changes in adhesion property during storage or during use. Furthermore, it may be desirable to further incorporate certain additives into the adhesive composition which can be utilized to provide benefits to attachment surfaces, particularly additives such as medications and skin enhancers.